Thermostatic switch enclosed in a receptacle



Oct. 24, 1950 H. szABc5 THERMOSTATIC swrrcu ENCLOSED IN A ascsp'mcua Filed Aug. 27, 1946 amen war/0M 5 Z a Z9 5 Patented Oct. 24, 1950 'r'n nMos'rA'rio swrroHnNCLosEn INA I 1 RE E CP Henrik S'zab; Stockholm, Sweden; assignor' to T'Ielefonaktiebolaget L M- Ericsson, Stockholm, Sweden, a company of Sweden Application August 27, 1946, Serial No. 693,249 a In Sweden September 19, 1945 This invention relates to thermo-contact devices; such as are employed, for example, in connection with fire alarm installations to initiate operation of the alarm mechanism.

It mayhap'pen that the thermo-contacts of automatic fire alarm installations have to be placed in damp rooms or in places containing corroding or explosive gases. The usual kinds of enclosed alarm contacts cannot then be used since they become affected bythe damp or by the gases and if located in places containing explosive gases, they may produce an igniting spark at the moment of breaking. When used in such localities the contacts are therefore placed in closed glass or metal receptacles, in addition to which they are very often required to comply with the following conditions namely, the contact members should be soldered together and breaking of said contact should not be imperilled if the tension of the springs used to separate the contact members should depreciate due to ageing of the springs or the like; the operating time must be short; and manufacture and mounting must be simple and inexpensive. Preferably the device should be such, on the occurrence of a fire, to show visually whether it has functioned.

The present invention has for an object to provide a thermo-contact arrangement satisfying simultaneously all these conditions and in accordance therewith the contact members are soldered together by means of easily fusible metal alloy, one of said members comprising a sheet of metal closely fitting the inner wall of the receptacle and the other member comprising a bimetallic strip of which one end is fixedly mounted within said receptacle.

In order that the invention may be clearly understood and readily carried into effect the same will hereinafter be more fully described with reference to the accompanying drawings, which shows an embodiment for a two-wire plant with bimetallic strips, and in which Figure 1 is a longitudinal section on line a-a of Figure 2, through a glass bulb enclosing the strips; and

Figure 2 is a cross-section through the bulb.

Figure 3 is a diagrammatic view of a thermocontact connected to an alarm circuit.

Referring to the drawings, I indicates the glass bulb within which two metal sheets 2 are arranged close to the inner surface of the bulb. In many alarm-installations the alarm-circuit is a two wire-circuit outgoing from an alarm station and passing through the rooms to be protected and going back to said station, current passing through 4 Claims. (01. 200-438) both said wires and each of the wires being controlled by a contact in the thermocontact. For each-wire I, I and II, II of the alarm circuit is now provided a metal Sheet 2 (2") and a bimetallic strip 3 (3) and a spring-strip 5 (5). The current in line I passesterminal a, strip 3, soldered contact point 4, sheet 2, strip 5 and terminal b and then continues through line I, to a suitable alarm station. Current from wire II passes terminal C, strip 3, soldering point d, sheet Z, strip 5' and terminal (1 and continues in-line IIv to the alarmstation. Of course it is not necessary to use spring-strips 5 and 5' to connect the sheets 2 and 2 to terminals 17 and d. a, flap of the sheets instead could be connected to terminals b and d but if the metal-sheets 2 (2') are very thin, e. g., they are formed by metallizing the inner wall of the receptacle, such a connection would be difiicult to perform and the arrangement suggested, i. e., to let a spring-strip 5 (5) press against the sheet (and possibly be soldered thereto), would be more advisable. Each thermocontact thus controls separately wire I and II of the alarm circuit.

The purpose of sheet 2 (2') is to absorb the heat from outside and transmit it to strip 3 (3) which serves as a contact breaking member, the purpose of strip 5 (5) only being to electrically connect sheet 2 (2') to terminal b (d) to which last-mentioned the wires I and II outgoing to the alarm station are to be connected. The strips are arranged symmetrically (see Figure 2), so that they will not come into contact with each other on bending.

When the temperature increases, the heat absorbed by the metal sheets 2 is transmitted through the solder joints to the bimetallic strips, which are heated and thereby tensioned in a direction away from the wall of the bulb. When a certain temperature is attained, the soldering metal melts and the bi-metallic strips bend away from the wall, the circuit thereby being broken and the strips occupying the positions shown in broken lines in Figure 1. In case the bimetallic strips are given a certain pretension, thereby tending to move from the wall of the bulb, their position, after a fire has broken out, will indicate whether the device has operated.

The metal sheets 2 may, for example, be fixed to the wall of the bulb by means of glue or in ome other suitable manner. It is also possible to form the metal sheets by metallizing the inner surface of the bulb wall.

Since one pole of the soldered contact is constituted by the metal sheet 2 itself lying close to.

The mounting of the strips can advantageously be such that the ends thereof which are nearer to the base of the bulb are provided with 'internally threaded bushes 6 which extend through holes formed in an insulating plate 1 of, for example, mica, said plate, after springs have been soldered to the sheet, being supported by the strips inside the bulb. When the base is there- I after inserted into the end of the bulb before the latter is sealed, pole shoes 8 formed with holes, which shoes are fixed to the connection wires 9 protruding from the base-will take up such position that the holes therein will register with the holes in the bushes, the pole shoes being thereafter connected to the bushes by screws or bolts.

The bulb may then be sealed. The pole shoes 8 may possibly be replaced by a ring on the connection wires 9.

I claim: V l. Thermo-contact device comprising a recep tacle of insulating material, two contact members forming a contact point to be broken on heating, a metal lining arranged inside said receptacle and 4 closely fitting the inner surface of said receptacle, said lining forming one of said contact members, a heat sensitive strip of bimetallic material disposed within said receptacle, and forming the other of said contact members, means fixing a portion of said strip to as point being insulated from Saidlminaand easiiyiusible, solder securing another portion of said strip to said metal lining. 2. Thermo-contact device according to claim 1, wherein said bimetallic strip having pro-tension tends to move said strip inwardly away from said REFERENCES CITED The following referencesare of record in the file of this patent: 4

UNITED STATES PA'I'ENTS Number I Name Date 1,851,657 Appelberg Mar. 29, 1932 1,950,240 Hilgenberg Mar. 16, 1934 2,041,362 McIlveney May 19, 1936 2,413,140 Griffith Dec. 24, 1946 2,428,838 Derby Oct. 14, 1947 

